David Hughes is the Daily Telegraph's chief leader writer. He has been covering British politics for 30 years.

Beware the dodgy dossier

What is it about intelligence dossiers that make you want to pick them up with a pair of tongs?

Remember all the trouble this one caused?

The new National Intelligence Estimate compiled by the US government's 16 security agencies concludes that there is no nuclear weapons programme being actively pursued in Iran. It was suspended in 2003.Â Relief all round. The trouble is, the NIE published in 2005 said precisely the opposite, that Iran was developing nuclear weapons in the teeth of international pressure. They cannot both be right. Perhaps we should toss a coin.

The American intelligence community has form in this area. Remember former secretary of state Colin Powell's Iraq weapons dossier, unveiled at UN headquarters in February 2003, as the clinching argument for the subsequent invasion? At its heart were detailed descriptions of mobile labs for the production of chemical and biological weapons.

The trouble was, the whole thing was a fabrication. The intelligence was supplied by an Iraqi exile code-named Curveball (real name Rafid Ahmed Alwan). He claimed to be a prominent chemical engineer whereas he was, in fact, a taxi-driver and inveterate fantasist as the coalition forces found to their cost when they vainly scoured Iraq for the mythic mobile labs.

Of course this is not an exclusively American problem. Who can forget Alastair Campbell's dodgy dossier, culled from the internet by his office staff? Or the barely more credible Joint Intelligence Committee dossier produced by the then head of the Joint Intelligence Committee, John Scarlett. He was punished with a knighthood and control of MI6.